"China's recent actions against Panama-flagged vessels raise serious concerns about the use of economic tools to undermine the rule of law in Panama," US Secretary of State Marco Rubio said in a statement.

The United States has accused China of detaining Panama-flagged ships in response to a takeover by Panamanian authorities of two canal ports previously run by a Chinese company.

Washington and Beijing accuse each other of seeking to control the Panama Canal, a vital trade link between the Atlantic and Pacific oceans.

"The United States stands firmly with Panama and looks forward to increasing our economic and security cooperation with this important partner," Rubio said.

Chinese foreign ministry spokesman Lin Jian said China's position on the port was "clear-cut" when he was asked about the ship detentions at a press briefing on Friday.

"The US's repeated unwarranted comments only reveal its scheme to seize the canal," he said without directly addressing the accusations of ship detentions.